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-- 

-- Copyright (C) 2009, 2010 Dr. Juergen Sauermann

-- 

--  This code is free software: you can redistribute it and/or modify

--  it under the terms of the GNU General Public License as published by

--  the Free Software Foundation, either version 3 of the License, or

--  (at your option) any later version.

--

--  This code is distributed in the hope that it will be useful,

--  but WITHOUT ANY WARRANTY; without even the implied warranty of

--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

--  GNU General Public License for more details.

--

--  You should have received a copy of the GNU General Public License

--  along with this code (see the file named COPYING).

--  If not, see http://www.gnu.org/licenses/.

--

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--

-- Module Name:    Register - Behavioral 

-- Create Date:    16:15:54 12/26/2009 

-- Description:    the status register of a CPU.

--

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library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity status_reg is

    port (  I_CLK       : in  std_logic;

            I_COND      : in  std_logic_vector ( 3 downto 0);

            I_DIN       : in  std_logic_vector ( 7 downto 0);

            I_FLAGS     : in  std_logic_vector ( 7 downto 0);

            I_WE_F      : in  std_logic;

            I_WE_SR     : in  std_logic;

            Q           : out std_logic_vector ( 7 downto 0);

            Q_CC        : out std_logic);

end status_reg;

architecture Behavioral of status_reg is

signal L                : std_logic_vector ( 7 downto 0);

begin

    process(I_CLK)

    begin

        if (rising_edge(I_CLK)) then

            if (I_WE_F = '1') then          -- write flags (from ALU)

                L <= I_FLAGS;

            elsif (I_WE_SR = '1') then      -- write I/O

                L <= I_DIN;

            end if;

        end if;

    end process;

    cond: process(I_COND, L)

    begin

        case I_COND(2 downto 0) is

            when "000"  => Q_CC <= L(0) xor I_COND(3);

            when "001"  => Q_CC <= L(1) xor I_COND(3);

            when "010"  => Q_CC <= L(2) xor I_COND(3);

            when "011"  => Q_CC <= L(3) xor I_COND(3);

            when "100"  => Q_CC <= L(4) xor I_COND(3);

            when "101"  => Q_CC <= L(5) xor I_COND(3);

            when "110"  => Q_CC <= L(6) xor I_COND(3);

            when others => Q_CC <= L(7) xor I_COND(3);

        end case;

    end process;

    Q <= L;

end Behavioral;